1. Field of the Invention
The present invention generally relates to a transfer apparatus, a method for preventing a leakage current of the transfer apparatus, and an image forming apparatus including the transfer apparatus.
2. Description of the Related Art
In inkjet type image forming apparatuses (inkjet printers), images are formed by discharging ink onto recording paper that is moved on a paper transfer apparatus. When the recording paper is too thin or too much ink is discharged onto the recording paper, the ink impregnates the fibers of the recording paper. The fibers swollen by the ink causes the recording paper to be bent in a wrinkled state (the wrinkled state is referred to as “cockling”), and may cause the recording paper to be lifted. When the recording paper is lifted, landing positions of the discharged ink droplets are displaced from the predetermined positions or the recording paper contacts a recording head, resulting in drastically decreasing the quality of an image formed on the recording paper.
In order to prevent the recording paper from being lifted, various ways have been suggested such as using thick recording paper which is not swollen even when impregnated by the ink, using expensive paper coated with an ink absorbent which prevents impregnation of ink into a surface of the recording paper, drying the recording paper by hot air before the recording paper is swollen, forcibly drying the recording paper by heating a back side of the recording paper with a heater, or providing a guiding plate for preventing the recording paper from being lifted. However, these ways have disadvantages of leading to an increase in printing cost.
In view of this, an electrostatic attaching type paper transfer apparatus has been suggested to be applied, of which usage has been proven in a page turner or a paper transfer apparatus in an electrophotographic type image forming apparatus. In this paper transfer apparatus, a high voltage is applied to a transfer belt to generate an electrostatic force so that recording paper is forcibly attached onto the transfer belt, whereby the swollen recording paper is prevented from being lifted (for example, see Patent Document 1). According to this paper transfer apparatus, paper can be prevented from being lifted due to swelling without using a complicated mechanism, and images can be formed on the paper with high printing quality by hardly increasing the printing cost.
However, when an inkjet printer and the like sufficiently cooled over night in winter are exposed to warm air emitted from a heating appliance such as an air conditioner, a gas heater, and an oil heater in the morning, condensation may form on the surface of the transfer belt since the transfer belt at a low temperature is exposed to the warm and humid air. The condensation on the surface of the transfer belt leads to a leakage current generated when a high voltage is applied to the transfer belt. Normally, when a leakage current is generated in a high voltage power source system, the power of the apparatus is turned off in view of protecting the apparatus and ensuring safety. When a leakage current that is not significant enough to cause the apparatus to be turned off is generated, a control board is normally started and made ready to be used when the power of the apparatus is turned on. However, when an instruction to start printing is received and a high voltage power source board is turned on, a leakage current flows through the condensation on the surface of the transfer belt. A leakage detecting circuit provided in the high voltage power source detects this abnormality and registers an error. Such a phenomenon can be caused every morning in a specific period for a user in a cold region.
In view of this, a simple countermeasure to obtain reliable effect against such a phenomenon is in demand. For example, there is a known method to incorporate a condensation preventing heater, which has been employed in expensive electrophotographic type printers and the like. However, this method has defects in that manufacturing cost is increased so that inexpensive types of printers cannot easily employ this method, current is consumed when the power is off, and the condensation preventing heater does not work when the main power of the apparatus is off.
As a countermeasure for this method, Patent Document 2 discloses a method for preventing a current leaking from a transfer belt, from another point of view. In this method for preventing a leakage current, in the case where the image forming apparatus registers an error because of a leakage current caused due to condensation on the transfer belt when the apparatus is not operating, a high voltage power source is turned off and recording paper is transferred to the transfer belt so that the condensation (moisture) on the transfer belt is absorbed by the recording paper. Normally, plural sheets of recording paper are supplied onto the transfer belt and then transferred in an idle manner without undergoing image printing. This operation is repeated until the condensation all over the transfer belt is absorbed. As a result, the current leaking from the transfer belt is resolved. When the leakage current flowing from the transfer belt is resolved, a high voltage is applied to the transfer belt again, and a normal image forming operation can be performed.
According to the method for preventing a leakage current disclosed in Patent Document 2, a leakage current caused by condensation on the transfer belt can be prevented without significantly increasing the manufacturing cost and power consumption of the image forming apparatus. However, this method requires plural sheets of recording paper to absorb the condensation. In particular, in order to absorb the condensation all over the transfer belt, the plural sheets of recording paper are transferred in an idle manner until the whole surface of the transfer belt is contacted by the recording paper. In the case where the standard-sized paper sheets are used, there is an interval set between the transfers of the sheets of paper. Therefore, in order to transfer the recording paper to contact the interval part of the transfer belt, the transfer belt has to rotate plural times. In this case, many sheets of recording paper are wasted and a longer time is required.
Patent Document 1: Japanese Patent Application Publication No. 7-53082
Patent Document 2: Japanese Patent Application Publication No. 2006-16111